1. Field of the Invention
This invention relates to a flow control device for measuring the flow of fluids in relatively low flow levels such as gas, and shutoff valve apparatuses built into the mass flow control device mentioned above.
2. Description of the Related Art
Semiconductor devices such as semiconductor integrated circuits and the like are generally produced by using several types of semiconductor manufacturing devices to repeatedly carry out etching, CVD film formation or the like, on semiconductor wafers or the like. In such cases a mass flow controlling device such as a mass flow controller is used because of the need to precisely control the supply of trace amounts of processing gas. See, for example, patent document 1 (Japanese Patent publication No. 11-154022 A2) and patent document 2 (Japanese Patent publication No. 2006-38832).
The structure of common mass flow controllers is illustrated in FIG. 8. FIG. 8 schematically illustrates the structure of an example of a conventional mass flow controller inserted into a gas piping, and FIG. 8 is a circuit diagram illustrating the flow detection means in a mass flow controller.
As illustrated, the mass flow controller 2 is inserted into a flow path, such as a gas piping 4, through which a fluid such as a liquid or gas flows, so as to control the mass flow. A vacuum is created, for example, inside of a piping of the semiconductor manufacturing device connected to one end of the gas piping 4. The mass flow controller 2 has a flow path 6 formed by means of stainless steel, for example, both ends of which are connected to the gas piping 4. The mass flow controller 2 includes mass flow detection means 8 located in the upstream stage of the flow path 6, and a flow control valve mechanism 10 located in the downstream stage.
The mass flow detection means 8 has a bypass assembly 12 comprising a bundle of a plurality of bypass tubes located upstream in the direction in which the gas fluid flows in the flow path 6. A sensor tube 14 is connected to both ends of the bypass assembly 12 to bypass the assembly, allowing a smaller amount of gas fluid compared to the bypass assembly 12 to flow at a constant rate therein. That is, a constant proportion of gas relative to the total gas flow always flows into the sensor tube 14. A pair of control resistor wires R1 and R4 connected in series are wound around the sensor tube 14, and flow signals S1 indicating the mass flow level are output by a sensor circuit 16 connected thereto.
The flow signal S1 is input to a control means 18 formed using a microcomputer, for example. The mass flow of the gas currently flowing is determined based on the flow signal S1. The flow control valve mechanism 10 is controlled so that the determined mass flow is consistent with the mass flow represented by an input flow set-point signal S0. The flow control valve mechanism 10 has a flow control valve 20 located on the downstream side of the flow path 6. The flow control valve 20 has a diaphragm 22 made of bendable metal plate, for example, as a valve for directly controlling the mass flow of the gas fluid.
The diaphragm 22 is moved toward the valve orifice 24 by being appropriately bent and reshaped, to allow the aperture or the opening degree of the valve orifice 24 to be controlled as desired. The upper surface of the diaphragm 22 is connected to the bottom end of an actuator 26 formed using a laminated piezoelectric element (piezo element), thereby allowing the aperture to be adjusted in the manner described above. The actuator 26 is operated by means of the valve drive voltage S2 output by the valve drive circuit 28 upon receiving a drive signal from the control means 18. An electromagnetic actuator may sometimes be used instead of a laminated piezoelectric element as the actuator 26.
Although it is necessary to stop completely a gas flow into the semiconductor manufacturing device side depending on some cases, the complete stop of gas flow is difficult because the structure of the flow control valve mechanism 10 is suitable for the flow control, not for shutoff, in the mass flow control device 2 as described above. For this reason, the shutoff valve apparatus is commonly installed in the upstream or downstream or at both sides of the mass flow control device 2. Such shutoff valve apparatus is used also at the time of zero adjustment and calibration of the mass flow control device 2.
For example, as indicated in the patent document 1 and shown in FIG. 9, the shutoff valve apparatus 30 with the pneumatic piston-cylinder actuator is plumbed to the mass flow control device 2 separately.
FIG. 9 shows an example of the conventional piping form of a mass flow control device and the shutoff valve apparatus. The shutoff valve apparatus is connected to the downstream side of the mass flow control device separately therein.
Regarding a shutoff valve apparatus of a normally open type, the shutoff valve apparatus with the pneumatic piston-cylinder actuator can easily acquire a higher power than the actuator 26 by enlarging the air contacted surface area of the cylinder. Thus, the pneumatic piston cylinder actuator has the advantage in shutoff performance of the diaphragm valve.
However, since sealing components, such as O-rings, which are commonly placed between a piston and a cylinder of this kind of pneumatic actuator of the shutoff valve apparatus, interrupt the movement of the cylinder by the friction drag, the valve may not return to the open state only by the elastic repulsion force of the metal diaphragm. Therefore, it is necessary to have a spring, etc., as an auxiliary component to open a valve certainly.
For this reason, the valve actuator consists of many parts. The structure is complicated and the size is large.
Additionally, the capacity in the gas pipe 4A, which is a connected portion between the above-mentioned mass flow control device 2 and the shutoff valve apparatus 30, e.g., a few cc, cannot be ignored as the dead volume. Since the gas remaining in the portion is the gas which the above-mentioned mass flow control device 2 cannot control, when semiconductor manufacturing devices are operated, etc., that is, when a process is resumed after closing the above-mentioned shutoff valve apparatus 30, the above-mentioned remaining gas must always be discarded. Therefore, there is a problem that the wasteful consumption of processing gas is large.
Then, the manner of integrating the above-mentioned shutoff valve apparatus 30 into the mass flow control device 2 is also proposed (FIGS. 1-3 in the patent document 1. FIG. 9 in the patent document 2).
For miniaturization, the shutoff valve apparatus of the direct sealing type whose diaphragm is driven directly with the compressed operation gas is disclosed in the patent document 1.
The shutoff valve apparatus of the patent document 1 consists of the valve seat, which is made of resin and provided in the downstream side of a flow control valve, and the metal diaphragm, which is located in the opposed position to the valve seat and clamped between a valve body and a screw type lid member.
The valve is closed by forcing metal diaphragms to the valve seat made of resin directly with the operation air supplied from air piping connected through the tube fitting screwed to the lid member.
According to this structure, there is no part such as a piston, and there is no factor that interrupts the returning movement of the metal diaphragm to the original form with its elasticity when operation air is exhausted. For this reason, it is not necessary to have a spring, etc., for assistance of opening a valve. That is, structure can be simple and there can be few parts as compared with the shutoff valve apparatus of a piston-cylinder actuator. This enables the shutoff valve apparatus to be miniaturized.
Moreover, the mass flow control device with built-in shutoff valve apparatus is indicated in the patent document 2, as shown in FIG. 10. FIG. 10 is a cross-section schematic view showing an example of the conventional mass flow control device with built-in shutoff valve apparatus. The same reference mark is given to the component part and the identical configuration portion in FIGS. 8, 9 and 10.
The structure indicated in FIG. 10 is fundamentally the same as the structure shown in the patent document 1, in the point of being built-in of the shutoff valve apparatus of a direct sealing type. The flow control valve mechanism 10 has the metal diaphragm 22 and the actuator 26 which presses and bends the above mentioned metal diaphragm 22. The valve aperture is changed to control the gas flow by making the above-mentioned diaphragm 22 approach or move away from the valve orifice 24. The shutoff valve apparatus 30 is located in the downstream side of the above-mentioned flow control valve mechanism 10, that is, in FIG. 10, the shutoff valve apparatus 30 is opposed to the lower part of the flow control valve mechanism 10, for example, is mounted on it bar screw junction.
This shutoff valve apparatus 30 has the valve chest 36 connected with the above-mentioned valve orifice 24 through the inlet flow path 34, and this valve chest 36 is divided by the metal diaphragm valve element 38 formed in the shape of a typically spherical shell.
The inlet port of the above-mentioned inlet flow path 34 facing this valve chest 36 is an inlet valve port 42, and the valve seat 44 is located in the portion of this inlet valve port 42. And from this valve chest 36, the outlet flow path 40 is extended toward semiconductor manufacturing device. On both sides of the above-mentioned diaphragm valve element 38, the operation chamber 46 is located in the opposite side of the above-mentioned valve chest 36, and the compressed operation air can be supplied to this operation chamber 46 by the electromagnetic three-way valve 48.
The inlet valve port 42 is closed by sitting the above-mentioned diaphragm valve element 38 on the valve seat 44, bending the diaphragm with the above-mentioned operation air supplied to the operation chamber 46. Thereby, the flow control valve mechanism 10 controls the mass flow rate of a gas and the shutoff valve apparatus 30 shuts off a gas flow completely. And, the capacity of the inlet flow path 34 connected from the flow control valve mechanism 10 to the shutoff valve apparatus 30, that is, the dead volume is much smaller than that of the gas piping 4A portion of the conventional device as shown in FIG. 9. Therefore, the capacity of the out-of-control gas can be decreased.
By the way, the device, which was disclosed by the above-mentioned patent documents 1 and 2, can be miniaturized in its size and also has the advantage that there is little processing gas to discard, since the shutoff valve apparatus was integrally incorporated in the mass flow control device as explained with reference to FIG. 10.
However, in the example of device as shown in the above-mentioned FIG. 10, since the pressure of operation air is uniformly applied to the whole metal diaphragm valve element 38 when the diaphragm valve element 38 of the shutoff valve apparatus 30 is operated, the high pressure of the operation air is required for deforming the metal diaphragm valve elements 38 to a closed valve state.
For example, when the gas flow at pressure 0.3 MPa is cut off, the operation air pressure of about 0.6 MPa is required, but the pressure of the operation air generally used at the manufacture factory for producing the semiconductor manufacturing device is the range of 0.4-0.7 MPa. For this reason, there was a problem that it will become difficult to realize the full closed state when the pressure of the operation air of factory is the range of 0.4-0.5 MPa. Since it is necessary to boost the operation pressure of shutoff valve apparatus to cut off the flow of high-pressure gas certainly as mentioned above, the inconvenience which is obliged to big repair in the facility of semiconductor manufacturing factory arises.